Thread cutting tap



Marchls, 1932. E A, WALKER 1,849,894

THREAD CUTTING TAP Filed'Jan. 22, 1931 JQ 16 Y JL 17 17 A f l J3 v 9 Z55/917797' lf'laJzA 7VaZ/enl a, darauf:

of the nut and bolt, instead ofbeing parallel Patented Mar. l5, 1932 `STATE ERNEST A. WALKER, E WORCESTER, MASSACHUSETTsASsIGNoR To Joni: BATH; or

WORCESTER, MASSACHUSETTS A THREAD CUTTING TAP Application led January 22, 1931. Serial No. 510,516. 'Y y, Y

between the threads 13 of the bolt 11.are

'I his invention relates to a tap designed for cutting a special thread in a nut or1 other internally threaded device. In certain devices, such as a particularl type of lock nut, it is desirable to provide the inner end faces of the internal threads in the nut or device with a surface shaped somewhat differently from that which can be produced by boring or reaining a straight hole in the device. In one such lock nut, the inner surface of the threads in the nut is of a spiral conical form, producing a wedging action when moved relatively axially with reference to a bolt by engagement with a member to be secured.

i It is the object of my invention to provide a tap having cutting edges so designed as to produce a surface of a desired and special contour at the inner ends of the nut threads.A

A further object of my invention is to provide a tap in which alternate teeth of the tap shape the nut threads at the sides, while in tervening teeth of the tap clear the threads at the sides but shape the inner end surfaces of the threads. f I

My invention further relates to arrangement-s and combinations of parts which will be hereinafter described and more particularly pointed out in the appended claims.

A preferred formoflthe invention is shown in the drawings, in which Fig. 1 is a side elevation of a tap embody,- ing my improvements;

Fig. 2 is an end view thereof; Y f

F 3 is an enlarged detail sectional view of portions' of the nut and tap, and

4 is a sectional view showing a bolt in operative relation with a nut threaded by my improved tap. Y

Referring irst to Fig. 4, I have shown therein a nut 1() and bolt 11 of a commercial form, in which the thread grooves 12 of the nut 1() are of such size as to provide substantial clearance at the sides and bottom of the groove 12, with respect to the thread 13 of the bolt 11.

The inner surfaces 15 of the threads 16 on the nut are cut at an angle to the axis thereto as in the usual Acme thread, and the surfaces 17 at the bottom of the grooves 18M similarly inclined with respect to the axis-of the bolt. The lside clearance of the grooves in the nut with respect to the threads of the bolt allows limited aXial movement or adjustment of the nut'relative to the bolt.

If the nut is positioned so that the leading side surface 2O of thenut thread is adjacent to the side surface 21 ofthe bolt thread, the inclined surfaces and 17 will bevradially separated and the nut ,will turn .freely on the bolt. TWhen the nut engages a surface to be clamped, however, the nut will be forced axially along the bolt in the direction of the arrow a, thus causing the tapered inclined surfaces 15 and 17 to come into engagement with each other and to' firmly lock thenut on the bolt. f

` No particular difficulty is encountered in providing a bolt with the inclined or conical surfaces 17 between the threads 13, but substantial diiiiculty has been encountered in producing a nut withthe inclined `conical irfaces 15 at the inner ends of the threads In the working out of my invention, I have produced the tap shown in Figs. 1 to 3, which is effective for tapping a nut of the construction shown in Fig.' 4. l

In the drawings, I have shown a tap having a body grooved longitudinally to provide lands 31 (Fig. 2)' and I-preferably but not necessarily provide an uneven number of lands. Teeth 33 separated by grooves 34 are formed in the lands 31 by any usual cuttingorfgrinding operationv and the entering end of thetap is tapered as usual and as indica'tedat35.A jVv Q- In the preferred procedure of manufacture, I first fornil the tap by cutting a'groove 40 therein toproduce thesurfaces 41 and 42 at the sides ofthe thread 44 and the sur face 43 at the 'bottom or root of the groove 40. I then submit theV tap to a grinding or relieving operation'by which one groove 40 will be increased in depth to the line indicated at 45 in Fig. 3, and the next `groove 40 will becut away at the-sides to the lines indicated at 46' and 47 in Fig. 3. The lengthwise grooves between thelands are deep enough i grooves lengthwise of the lands 31, as well as spirally along the threads. y

Inthe use of my improved tap, the nut is first bored to an internal diameter indicated at; B in Fig. 3, the surface B being of less diameter than the inclined cutting surface 43. As the tap advances in the nut, the

threads 44 yof the tap cut Ya thread groove 12 (Fig. therein and leave threads 16 between the grooves, the threads then having a cross section like `the space between the side faces 41. and 42 of the tap and the inner surface B of the nut.

This inner surface B is then reamed or trimmed by the inclined cutting surface 43 at the bottom of the thread groove on the next following land lof the tap. The sides of the threads of the tap at each side of the surface 3 are cut away aty 46 and 47, so that the cutting edge 43 extends across and beyond the inner surface of the partially formed thread 16 -in the nut, thus providing a clear cutting edge for the full width ofthe thread.

It will be understood that the formation of the thread in the nut takes place in the usualmanner by removing` successive portions or layers (Fig. 3) from'the bottom of the'groove in the nut, until the desired depth of thread groove is attained, this being due to the tapered portion 35 of the tap. The bottom cutting edges 43 are alsoarra-nged at a slight taper so that successive thin chips are removed from the inner end faces of the threads.

Thus by a single tapping operation, I .provide a nut having a desired threadsectionl and also having` the inner faces of the threads cut in the form of a conical spiral for engagement with a similar surface on the special bolt 11 previously described.

The provision of side Vclearance, as indicated at 46 and 47, and bottom clearance as indicated at 45, is very important, asothery Wise the tap would be subject to much greaterV strains, and the corners ofthe threads in the nut would be rounded, instead of presenting the full width conical surface shown Ain the` drawings. Y

Having' thus described my invention and the advantages thereof, I do not wish to be limited tothe details herein disclosed, otherwise than as set forth in the claims, but what I claim is 1. A tap comprising a body deeply grooved longitudinally to provide a plurality of lands, Iand. cutting teeth and intervening thread grooves formed' in aA helical series on said e lands, alternate threadgrooves in said helical series being ofA the-width of the internal threads to be formed but of greater depth.

threads out by said tap to an interrupted helical conical surface.

2. A tap comprising abody deeply grooved longitudinally to provide a plurality of lands, and cutting teeth and intervening thread grooves Y formed in helical series on said lands, alternate thread grooves in said helical series .being ofthe width of the internal threads to be formed but of greater depth than said threads, and intervening thread groovesV of the tap being of greater width than the first-named groovesl but of less depth and each having a bottomV face inclined with respect to the axis of the tap and adapted to trini the inner end faces of the internal threads cut by said tap Vto an interrupted helical conical surface.

3. A tap comprising a body deeply grooved longitudinally to provide a plurality of lands, and cutting teeth and intervening Vthread grooves formed in a helical series on said lands, two kinds of thread grooves alternating in said helical series, with one kind of groove of a certain Width and depth vand having cutting faces at the sides only thereof,

ing cuttingfaces at the sides 1only thereof,

and with the second kindof groove of greater width and less depth and having a bottom face provided with a cutting yedge at the bot-V tom only of the thread groove and inclined with respect to the axisv of the tap. y In testimony whereof I have hereunto affixed my signature.

` ERNEST A. WALKER.

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